Interactions of Aspartame with Streptococcus Mutans. The proposed research involves a systematic investigation of the modes of interaction of the non-carbohydrate sweetener, aspartame, with Streptococcus mutans, the oral bacterium most directly involved with dental decay. The specific aims of the work are to make systematic measurements, under a variety of conditions, of the potentially anticariogenic properties of aspartame: active inhibition of growth, decreased production of acid and adherent carbohydrates, and increased sensitivity to antibiotics and antiseptic mouthwashes. Comparisons of the action of aspartame on the above properties will be made with activities of another noncarbohydrate sweetener, saccharin, as well as with sucrose, in similarly prepared cultures of S. mutans. Additional measurements will be made of the effects of aspartame on selected enzymes or an membrane transport properties S. mutans, in order to study the mechanism of the anticariogenic properties of this commonly used sweetener. The definition of conditions under which aspartame alone, or combined with saccharin, can actively inhibit cariogenic oral bacteria or increase their sensitivity to antimicrobial agents is valuable for developing new adjunct treatments for oral disease. Better understanding of the inhibitory mechanism of aspartame could also lead to improved drug design for these treatments. Experiments have been designed to test different sweeteners under aerobic and anaerobic growth conditions and using complex and chemically defined growth media. The sweeteners used in tests will be: control (no additions), aspartame, saccharin, sucrose, aspartame+saccharin, aspartame+sucrose, saccharin+sucrose, and aspartame+saccharin+sucrose. After incubation of test cultures in each growth condition, cell growth, acid production, and extra- and intracellular carbohydrate will be measured. Total cellular protein, pH change and titratable acid, and colorimetric analysis respectively, will be the analytical techniques used. Sensitivity to specific antimicrobials will be determined by subculturing the organisms on agar plates and measuring growth inhibition zones around discs saturated with the test substance. Tests of interactions of aspartame with cellular enzymes will be made with centrifugally prepared cell-free extracts. Glycolytic enzymes and other enzymes will be assayed. To test possible interaction of aspartame with cell membranes, tests of uptake of trace metals essential for S. mutans will be measured. Membrane lipids will also be examined.